Rating:
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MRL - Clark Fork River Bridge No. 2

Photos 

MRL - Clark Fork River Bridge #2

View from the northwest

Photo taken by David Jones in April 2016

Enlarge

BH Photo #353726

Street View 

Description 

Relocated from unknown location. Information from NPRHA.org Online Collection

Facts 

Overview
Lattice deck girder bridge over Clark Fork River on Railroad (MRL)
Location
Missoula, Missoula County, Montana
Status
Open to traffic
History
Built 1896 at an unknown location, moved here 1929
Builder
- Pencoyd Iron Works of Pencoyd, Pennsylvania
Railroads
- Montana Rail Link (MRL)
- Northern Pacific Railway (NP)
Design
Lattice deck girder
Dimensions
Length of largest span: 100.0 ft.
Total length: 418.0 ft.
Approximate latitude, longitude
+46.87413, -114.00515   (decimal degrees)
46°52'27" N, 114°00'19" W   (degrees°minutes'seconds")
Approximate UTM coordinates
11/728212/5195531 (zone/easting/northing)
Quadrangle map:
Southwest Missoula
Inventory number
BH 58024 (Bridgehunter.com ID)

Update Log 

  • January 30, 2020: Updated by John Marvig: Added information from NP bridge records
  • May 19, 2016: New photos from David Jones
  • September 15, 2013: Added by Luke Harden

Sources 

  • Luke
  • David Jones - david2jpix [at] yahoo [dot] com
  • John Marvig - marvigj27 [at] gmail [dot] com

Comments 

MRL - Clark Fork River Bridge No. 2
Posted January 13, 2019, by John C Stutz (john [dot] stutz [at] spcrr [dot] org)

These spans are actually plate-lattice deck girders, a type that may be unique to the Northern Pacific railroad of the middle 1890s. This plate lattice type was originally used on the NP main, for replacing first generation wooden Howe truss bridges. See "Standard Plans for 100-Ft. Through Plate-Lattice Girder Bridges; No. Pac. Ry." in Engineering News of July 8 & 15, 1897 for design motivations, drawings, and details.

NP's several plate-lattice designs were briefly their standard for both deck and through girder bridges in the 85' to 105' range. The type apparently fell out of favor as locomotive weights increased, probably due to the difficulty of strengthening the lattice section. Main line spans would have gradually been recycled to branch lines, probably by circa 1905-15. An original through plate-lattice girder, initially installed at Lightening Creek near Clark Fork Idaho, which carried builder's plates naming it as such into the 1970s, ended at Orofino Idaho on the Camas Prairie's very lightly rated Kamiah branch.

These Missoula spans represent a further reuse, made by partially dismantling several original twin girder deck spans, replacing the lateral bracing, and reassembling them as triple girder spans. I suspect this occurred during the 1930s. The resulting capacity increase, from about E-33 to E-50, would have strengthened them sufficiently to carry the branch line engines that originally displaced them from the main. There may still be a second example, located about 1.5 miles north of Palouse, Washington, along highway 27. I am not aware of any others.